Pests thrive with climate change

Aug. 26, 2013

A truck sprays adulticide to control the mosquito population in Piketon in June 2011. Scientists say climate change awakens insects earlier in the season, leading to problems not just for quality of life but agriculture as well. / Frank Robertson/CentralOhio.com

Written by

Russ Zimmer

CentralOhio.com

A bagworm cocoon hangs from a branch on a juniper tree. Bagworms are common pests that can kill conifers and some deciduous trees. A few decades ago, these moths were found only in southern Ohio, but have since spread across the whole state as winter temperatures have moderated. / Ohio Department of Natural Resources

Ohio’s changing climate

To show how Ohio’s climate and environment are changing, the Media Network of Central Ohio sought concrete examples showing the state’s environment isn’t what it used to be, regardless of the cause. During the course of a week, the series will present several of these examples, but we know we can’t hit them all. If you have a story about the environment to share, tell us via our Facebook page. All the stories from the series will be posted to LancasterEagleGazette.com/climate as they appear online or in print.

A patch of kudzu, an invasive weed, engulfs trees near Wayne National Forest in this 2008 photo. / U.S. Fish and Wildlife Service

Ambrosia beetle / U.S. Department of Agriculture, Forestry Service

Next time you swat at a mosquito in early March, remember that it wasn’t always this way.

Climate change is responsible for the escalation of relatively warm days in winter, meaning bugs of all kinds begin to stir earlier in the year than historic norms.

Mosquitoes, like all insects, are very sensitive to changes in temperature. Their development — when they hatch, how quickly they grow and when they die — is dependent on it.

“The insect has to accumulate so much heat energy to meet certain points in its life cycle,” said Dan Herms, chairman of Ohio State University’s Entomology Department.

Fifty degrees is a good approximation for most bugs.

“The higher it is above that temperature, the faster the insect grows,” he said.

Putting the winter coat away in February might seem like an unassailable positive, but it also means those pesky bloodsuckers could be biting from before spring — winter officially ends March 19 next year — until the first frost of the fall.

“Mosquitoes of all different species, if you start their life cycles earlier in the spring, there will be the potential for more generations into the fall,” said Curtis Young, an entomologist at the OSU Extension in Van Wert County.

Aside from being a nuisance, mosquitoes are carriers of disease. There were 857 confirmed cases — leading to 59 deaths — of West Nile virus in Ohio from 2002 through 2012. Mosquitoes can pass other viruses, such as encephalitis, to humans and even transmit the heartworm parasite to dogs.

Beyond the unseasonable early-year temperatures, the softening of the harsh Ohio winter extends the range of pests that were once kept in check by the state’s frosty temperatures.

Bagworms, the bane of conifer trees, were unable to penetrate deep into Ohio decades ago because, when the temperature dips below 10 degrees, their eggs would freeze and die, Young said.

“When I first came into Ohio in 1982 to start my graduate work at OSU, the bagworm’s northern limit in the state of Ohio was Interstate 70,” Young recalled. “As of today, the bagworm’s northern limit is into Michigan.”

But mosquitoes and bagworms are only part of the picture. Some other examples of how climate change is paving the way for pests in Ohio are:

• The European corn borer and the black vine weevil — scourges of farms and nurseries, respectively — are both waking up earlier in the season.

The European corn borer enters into a corn stalk in its larval stage and exits as a moth. In between, it can cause serious damage to the crop. Herms said this pest is on the cusp of adding another generation, which would multiply its damage.

The story of the black vine weevil serves as a lesson in how climate change is forcing a thorough evaluation of pest control strategies in the commercial realm.

“(Nurseries) would spray based on these schedules that were based on research developed in the early ’70s,” Herms said. “Their pest management programs were failing, and they didn’t know why. Initially, they thought the insect had developed resistance to the pesticide. What was happening was (the weevil) was emerging three weeks earlier than they were doing in the 1970s.

“You have to control them before they lay their eggs, and so many eggs had already been laid”

• Severe weather events can predispose a tree to attack from wood-boring insects, according to research from Chris Ranger, a research entomologist with the U.S. Department of Agriculture in Wooster.

Ranger said flood-stressed trees were found to be more susceptible to attack from the ambrosia beetle, which tunnels into the trunk and deposits fungal spores that eat the tree from the inside out.

• Humidity is expected to be worse as global warming marches on. That’s a more favorable environment for fungi and molds, said Jim Hoorman, an OSU Extension educator in Putnam County.

“This is going to have an effect on grain storage especially,” Hoorman said.

• Invasive weeds also have crept north as Ohio’s harsh winters have softened.

Kudzu, a high-climbing vine that smothers native plant life, was colloquially known as “the vine that ate the South,” and it was always assumed Ohio’s winters would keep kudzu out. Its presence has been confirmed by the USDA in several southern Ohio counties in the past decade.

A report from the National Climate Assessment Development Advisory Committee, a consortium of federal government agencies, says “(agricultural) pests may have increased overwinter survival and fit more generations in a single year,” although the report states its unclear whether agriculture in all regions will be negatively affected. The committee described the pest evidence as suggestive and called for more study in the area.

Still, it’s not only academia that has noticed the changes. Hoorman said he is having such conversations more and more with farmers.

“We are starting to talk about extreme weather, how these changes are going to keep on occurring,” Hoorman said. “We’re talking about it a lot more than what we would before.”

OSU environmental economics professor Brent Sohngen said proliferation of insect pests is not among the most worrisome effects of climate change.

Controlling pests is something people have been able to do historically, and humans will continue to adapt tactics and technology, he said. Other byproducts of a warming planet are out of human hands, he added.